Concentricity, ovality, waviness, and out-of-plane features characterize a geometric surface. Such characterizing features are used in a number of applications; one in particular involves measuring a valve seat relative to a valve guide cavity of an engine's combustion chamber. Wherein, a valve reciprocates in the valve guide to open and close intake and exhaust passages, which communicate with engine cylinders. The valve seat is a tapered surface that facilitates seating the valve head in the intake and exhaust passages from the cylinders during the compression and power strokes of the engine.
When the valve head does not properly fit in the valve seat, the intake passage and the exhaust passage will riot be sealed properly during the compression and power strokes, thus causing power loss, reduced fuel economy, rough engine idling and increased pollution. Poor sealing also reduces the valve head and valve seat life by allowing hot exhaust gasses to leak and contact the valve surfaces and the valve seats. In order to promote seal quality, it is desirable to have the valve guide and the valve seat centers closely aligned along a common center with minimal error in ovality, waviness, and out-of-plane parameters.
The invention claimed herein improves upon known prior art, including Pierce et al. (U.S. Pat. No. 5,533,384). Pierce teaches a measuring device having contact with a surface to be used in relation to measuring concentricity. Pierce lacks the ability to repeatedly reproduce the datum axis using a non-contacting fluid pressure gap. The present invention improves upon Pierce by increasing accuracy of concentricity, ovality, waviness and out-of-plane by having a repeatedly reproducible datum axis that is generated using a non-contacting fluid pressure gap.